Electron gun assembly with control grid attached by bars to carrier ring



Jan. 23, 1968 A. KRAUS 3,365,603

ELECTRON GUN ASSEMBLY WITH CONTROL GRID ATTACHED BY BARS TO CARRIER RING Filed July 13, 1966 INVENTOR Ar/ur flaws ATTYS.

Patented Jan. 23, 1968 3,365,663 ELECTRON GUN ASSEMELY WITH CONTROL GRID ATTACHED BY BARS T0 CARRIER RING Artur Kraus, lVIunich, Germany, assignor to Siemens Aktiengesellschaft, Munich, Germany, a corporation of Germany Filed July 13, 1966, Ser. No. 564,873 Claims priority, application Germany, July 19, 1965, S 98,301 10 Claims. (Cl. 313-82) The invention relates to a beam generation system for electric discharge vessels, particularly high power tubes, in which the cathode and Wehnelt electrode (beam formation electrode) are completely shielded, being arranged in a metal cylinder of greater length which serves as a carrier tube and as the first accelerating anode, with the cathode being in the form of an indirectly heated supply cathode, particularly a metal capillary cathode, and the heaters being formed so as to be selfasupporting.

The invention is of special importance in high power tubes operating with electron beams. In this type of tube, for example, traveling wave tubes with high output, a considerable difliculty arises in keeping electrodes which are required for the beam formation, especially those directly adjacent to the cathode, sufiiciently cool that even in the event of a vapor deposition with emission promoting substances, such electrode will produce no thermal emission. This maintenance of coolness requires measures by which the heat given off from the cathode is reduced to the smallest possible amount. At a given cathode temperature the amount of heat given off, or the amount of heat absorbed by the adjacent control electrode, depends upon the magnitude of the surface of the cathode involved with respect to the heat radiation taking place and on the heat conduction through the unavoidable mechanical connections to the supporting elements.

With present demands and, above all, to be expected in the future, on the specific emission of a cathode, the cathode temperature must be raised above 1100 C. Probably the most prevelant manner of heating a cathode with the lowest losses is the cemented-in heater arrangement. Since the presence of electrolysis phenomena within the insulation material depends on the operating cathode temperature, not directly, but exponentially, in production cathodes which are operated with elevated emission temperatures corresponding difiiculties have already arisen. For this reason, a heater constructed as selfsupporting, from which the useful heat, however, can be given off only over the radiation process, must, to insure a reasonably supportable efficiency at correspondingly high output, be brought to as high as possible a temperature, i.e., of about 1600 C. to 1700 C. It is here more or less unavoidable that a considerable portion of the heat generated will be radiated as waste heat to directly adjacent electrodes, such as the Wehnelt electrode and the first accelerating anode. On the other hand, the waste heat cannot be conducted off directly to the tube shell (vessel wall), since between such shell and the first anode there exists practically the full anode voltage of, for example, several 10 kv. and, therefore, correspondingly a sufficiently great distance therebetween (insulation space) is necessary.

The problem, therefore, underlying the invention resides in special constructive measures, making use of especially well suited materials, to maintain the beam formation electrode immediately surrounding the cathode, in particular a Wehnelt electrode, as cool as possible, so that even with vapor deposition of substances capable of emission during operation it can generate no thermal emission, without, however, impairing the insulation properties between the individual electrodes.

This is achieved in a beam generation system according to the invention such as initially described by an arrangement in which the Wehnelt electrode consists substantially of a frontal iris (diaphragm) and a metal ring (carrier ring) uniformly spaced therefrom, which are connected by a number of metal bars distributed, in particular, uniformly, and running axially parallel, in cagelike formation, with the length of the bars being about equal to the length of the radiation protective casing or jacket of the cathode.

In the arrangement, there can be used to particular advantage, in view of the heat radiation, flat bars as the rods of such cage, whose fiat or curved surfaces are generally radially disposed. Aside from the objective of a minimum heat absorption, however, in special cases, for example in view of electrostatic field strengths developing in the presence of very high voltages, the ceramic bars, in an especially advantageous manner, may be constructed with a circular cross section.

In a further advantageous development of the invention, the Wehnelt cage with its carrier ring is secured directly below the cathode radiation protective jacket on a base ring inserted in the carrier tube, utilizing at least three, preferably five, insulating bars, and in this arrangement the cross sectional configuration and material of the bars is so selected that a sufiicient heat flow will take place to the base of the discharge vessel or to the carrier tube, consisting of copper. A preferred material for the insulating bars, normally made of oxide ceramic material, such as for example, aluminum oxide, is beryllium oxide. By reason of its greater heat conductivity, with use of insulating bars of beryllium oxide there can be achieved a heat dissipation increased up to five times. The base ring advantageously may be utilized simultaneously for the support of the cathode by securing the cathode thereto by means of separate ceramic bars in such a way that the fastening points of the ceramic bars of the two electrodes alternate about the circumference of the ring. Such ceramic bars, normally made of aluminum oxide, also can be made of beryllium oxide in connection with the installation of a heat brake on the cathode radiation protective cylinder. For the shielding of the ceramic bars against a vapor deposition with electrically conducting substances from the cathode or from the heater, the cathode support flange is advantageously extended downward by means of a metal cylinder.

Further details of the invention are explained with the aid of the example of construction illustrated purely schematically in the figure of the drawing. Parts which do not contribute directly to the understanding of the invention have been omitted therefrom or remain undesignated.

In the figure the reference numeral 1 designates an elongated metal carrier tube, preferably of copper, which serves as the first acceleration anode and is therefore constructed at its end face as a iris (diaphragm). Fully shielded within the interior thereof is a centrally arranged indirectly heated cathode having an emission substance carrier disk or plate 2 and a radiation protective shell 3, the extension 4 of which is constructed as a heat brake. Parts of the cathode not specifically represented are the cathode body proper, which in the following case comprises a supply container, closed off by a porous emission plate, and the heating space provided for the accommodation of the heater. Disposed in front of or extending around the cathode, that is, between the first acceleration anode and the cathode, is the beam formation electrode, i.e., the Wehnelt electrode. Its surface has been greatly reduced, without, however, impairing its electrical functioning, and it comprises substantially a frontal iris (diaphragm 5) and a carrier ring 6 uniformly spaced therefrom, which are connected and thus spaced by a number of metal bars (Wehnelt bars) 7. Through such cage like construction of the Wehnelt electrode it is achieved that only a small portion of the waste heat radiated from the cathode in the zone of the radiation protective jacket passes to parts of the Wehnelt electrode. Rather, the cathode cylinder surface largely radiates its waste heat between the Wehnelt bars directly upon the carrier tube 1, which, constructed as a copper tube, conducts the heat to the base end of the tube, where the heat is then finally dissipated by a radiator and corresponding cooling air. Most advantageously, with respect to the radiation conditions, the bars 7 are constructed as flat bars whose flat or curved surfaces extend in radial directions. However, in view of the electrostatic field strengths, developing at high voltages, a circular cross section can offer certain advantages. The length of the bars is so selected that the Wehnelt cage has a length approximately equal to that of the radiation protective casing or jacket proper of the cathode. The Wehnelt cage, with its carrier ring 6, is carried by a base ring 8 mounted in the carrier tube 1 disposed in the embodiment illustrated below the radiation protective casing of the cathode or its extension, and secured to the base ring by at least three, preferably five, ceramic bars. The number, cross section and material of the insulating bars are so selected that there is assured, a suflicient heat flow thereover to the lower part of the carrier tube. The bars consist of an oxide ceramic material, such as, for example, aluminum oxide, but for an increase of the heat'flow and thereby for the reduction of the determinative temperature differences occurring, they are, in an especially advantageous manner, made of beryllium oxide whereby a very low temperature may be achieved on the Wehnelt electrode.

The cathode, comprising elements 2, 3, 4, etc., is secured with its cathode support flange 19 to the base ring 8 in a similar manner, that is, with oxide ceramic bars in such a way that on the circumference of the ring the fastening points of the ceramic bars of the two electrodes, namely the Wehnelt electrode and the cathode, alternate. Such insulating bars, which likewise are generally made of aluminum oxide, can also be made of beryllium oxide in cases in which the heat output is particularly great, amounting, for example, to 1100 w., with the beam formation electrode, namely the Wehnelt electrode, being maintained irrespective thereof at an especially low temperature. This measure is particularly advantageous if the "lower part of the radiation protective casing or jacket of the cathode is subdivided in such a Way that the part extending up to the cathode support flange is constructed in the form of a heat brake, for example, of a VZA-foil cylinder. However, since such a heat brake is effective, i.e., provides for a considerable heat or temperature drop when a corresponding amount of heat flows over it, the utilization of insulating bars or beryllium oxide is then especially advantageous. For example, with the use of beryllium oxide bars with a heat output of 100 w. it is directly possible to lower the temperature of the Wehnelt iris (diaphragm) from 850 C. to 300 C. For the achievement of a sufficient shielding of the two groups of ceramic insulating bars against electrically conducting vapor deposition coatings from cathode and heater, advantageously the cathode support flange it} is provided with a downwardly extending cylindrical part 12. In the arrangement described, the entire waste heat fiows over the copper carrier tube 1 to the base end of the tube, not specifically illustrated, at which it is finally conducted from the discharge vessel by means of a corresponding radiator.

Changes may be made Within the scope and spirit of the appended claims which define what is believed to be new and desired to'have protected by Letters Patent.

I claim:

.1. A beam generation system for electrical discharge vessels, especially high power tubes, comprising a cathode and a Wehnelt electrode, a longitudinally extending metal cylinder forming a carrier tube and the first acceleration anode of said system, said cathode and Wehnelt electrode being disposed in and shielded by said tube, said cathode being of the indirectly heated suply type, such as a metal capillary cathode, with a heater of self-supporting construction, said cathode having a radiation protective casing, said Wehnelt electrode comprising a'frontal iris (diaphragm) a metal carrier ring uniformly spaced therefrom in the direction of the axis of said' tube, and a plurality of metal bars extending between and connecting said carrier ring and said frontal iris (diaphragm), whereby the latter is supported by said ring, the length of said bars being about equal to the length of the radiation protective casing of the cathode.

2. A beam generation system according to claim 1, wherein said frontal iris (diaphragm) is substantially ringshaped, the latter, said carrier ring, and cathode respectively operatively disposed on the axis of said tube with said metal bars being symmetrically disposed about, and extending parallel to said axis, forming a cage-like structure.

3. A beam generation system according to claim 1 wherein, said metal bars are in the form of relatively flat bars whose opposite face surfaces extend relatively radially with respect to said axis.

4. A beam generation system according to claim 1 wherein said metal bars have a circular cross section.

5. A beam generation system according to claim 1, comprising in further combination a base ring mounted in said carrier tube and disposed below said radiation protective casing of said cathode, means operatively connecting said carrier and base rings whereby the latter forms the support for the Wehnelt electrode, and at least three insulating bars operatively connecting said base ring and said cathode forming the support for said cathode, the materiahcross section and number of bars being so selected to provide predetermined heat flow thereover.

6. A beam generation system according to claim 1, wherein the insulating bars for the Wehnelt electrode consist of an oxide ceramic material, such as aluminum oxide, magnesium oxide, and especially beryllium oxide.

7. A beam generation system according to claim 5, wherein the means connecting said carrier ring with said base ring comprises a plurality of insulating metal bars, the number of such bars being equal to the number of bars connecting said base ring and cathode, with the respective attachment points of the cathode bars to the base ring being disposed between adjacent attachment points thereto of the bars for the Wehnelt electrode.

8. A beam generation system according to claim 5 wherein the insulating bars for the cathode consist of an oxide ceramic material, especially of beryllium oxide.

9. A beam generation system according to claim 1, comprising in further combination a heat brake in the form of VZA-foil cylinder, operatively disposed between the radiation protective casing of the cathode and the supporting means for the cathode.

10. A beam generation system according to claim 1, comprising in further combination a cylindrical part, said cathode having *a support flange to which cathode bars are connected, said cylindrical part extending from said support flange and forming a vapor deposition protector for both groups of insulating bars extending from: said base ring.

References Cited UNITED STATES PATENTS 2,828,437 3/1958 Dailey 3l382 X ROBERT SEGAL, Primary Examiner.

JAMES W. LAWRENCE, Examiner. 

1. A BEAM GENERATION SYSTEM FOR ELECTRICALLY DISCHARGE VESSELS, ESPECIALLY HIGH POWER TUBES, COMPRISING A CATHODE AND A WEHNELT ELECTRODE, A LONGITUDINALLY EXTENDING METAL CYLINDER FORMING A CARRIER TUBE AND THE FIRST ACCELERATION ANODE OF SAID SYSTEM, SAID CATHODE AND WEHNELT ELECTRODE BEING DISPOSED IN AND SHIELDED BY SAID TUBE, SAID CATHODE BEING OF THE INDIRECTLY HEATED SUPPLY TYPE, SUCH AS A METAL CAPILLARY CATHODE, WITH A HEATER OF SELF-SUPPORTING CONSTRUCTION, SAID CATHODE HAVING A RADIATION PROTECTIVE CASING, SAID WEHNELT ELECTRODE COMPRISING A FRONTAL IRIS (DIAPHRAGM), A METAL CARRIER RING UNIFORMLY SPACED THEREFROM IN THE DIRECTION OF THE AXIS OF SAID TUBE, AND A PLURALITY OF METAL BARS EXTENDING BETWEEN AND CONNECTING SAID CARRIER RING AND SAID FRONTAL IRIS (DIAPHRAGM), WHEREBY THE LATTER IS SUPPORTED BY SAID RING, THE LENGTH OF SAID BARS BEING ABOUT EQUAL TO THE LENGTH OF THE RADIATION PROTECTIVE CASING OF THE CATHODE. 